What are Rubies and Sapphires chemically known as?

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Q: 113 (IAS/2008)
What are Rubies and Sapphires chemically known as?

question_subject: 

Science

question_exam: 

IAS

stats: 

0,43,80,46,43,17,17

keywords: 

{'sapphires': [0, 0, 1, 0], 'rubies': [0, 0, 1, 0], 'silicon dioxide': [0, 0, 1, 0], 'aluminium oxide': [0, 1, 1, 0], 'boron nitride': [0, 0, 1, 0], 'lead': [7, 1, 11, 11]}

Rubies and Sapphires are both varieties of the mineral corundum, which is chemically an aluminum oxide (option-2). Therefore, option-2 is the correct answer.

Option-1 (Silicon dioxide) is incorrect as it is not the chemical composition of Rubies or Sapphires, it is rather the chemical name for quartz.

Option-3 (Lead tetroxide) is not correct because it is not related to gemstone composition. It is a highly toxic, bright red or orange crystalline compound.

Option-4 (Boron nitride), though used in industrial applications due to its high thermal and chemical stability, it is not the chemical substance that Rubies and Sapphires are composed of.

The key difference between rubies and sapphires is the impurity present in the aluminum oxide; if it`s chromium, the stone is a ruby, and if it`s iron or titanium, the stone is a sapphire.